Treatment of unbleached cellulose pulps



Jan. 22, 1963 Filed July 24, 1959 M. D. STRONG TREATMENT 0F: UNB'LEACHEDCELLULOSE PULPS 4 SheatsSheet 1 Fig.

INVENTOR Michael D. Strong ATTOR EY Jan. 22, 1963 M. D. STRONG TREATMENToF UNBLEACHED cELLuLosE PULPs Filed Jly 24, 195s 4 Sheets-Sheet 2 v n wfo/0 mmo ve W WHW/Mm M l' o Ll *N Jan. 22, 1963 M. DQ STRQNG 3,074,842

TREATMENT OF I-JNBLEACHED CELLULOSE PULPS Filed July 24, 1959 4Sheets-Sheet 3 -r- SUCOH GIO2 Gas INVENTOR Jan. 22, 1963 M, D. STRONG3,074,842

TREATMENT oF UNBLEACHED cELLULosE PuLPs Filed July 24, 1959 4Sheets-Sheet 4 FIG. 5

[lilllllHlllIl'llllllllIllllllllllllllIIII||||ll||||||l||IIIIIIIIIIIIHIIlllllINVENTOR. 0 IO 20 30 40 50 60 70 80 Miche| D Strong TORNE Y MillimeterUnited States Patent- Oliver Incorporated, Stamford, Conn., acorporation of Delaware Filed July 24, 1959, ser. No. szazsa 17 claims.(ci. 162-66) This invention relates to the purification Iand bleachingtreatment of cellulose pulps produced from :wood chips by variousinitial treatment processes. For example, this may be so-called brownstock which is the result of chemical digestion of wood chips in acooker, or stock which has resulted from semi-chemical treatment of thechips such 4as the neutral sulite semi-chemical process involvmg lacombination of chemical and mechanical effects, or stock which may havebeen obtained from mechanical pulping treatment alone. For the purposesof this invention, all these pulps are herein collectively termedunbleached pulps. If this pulp has undergone additional partialtreatment, it will herein be termed partially bleached stock.

Such unbleached pulps contain the separated wood bers or ber bundlesstill burdened or coated with noncellulosic 'binding substances `whichmust be removed with as little mechanical `damage or chemicaldegradation as possible indicted upon the bers themselves, to the end ofobtaining clean bleached bers with a minimum of debris as a basis -forproducing high grade strong and flawless paper.

As distinct from the conventional treatment of such dilute pulps inreaction towers, this invention revolves around the discovery that Ibyspecial treatment in a novel manner such pulp can be dewatered andconverted into spongy units or flocs physically so conditioned thatgaseous reagents such as chlorine in its gaseous state can beeffectively employed. The desired reaction of the gas with thenon-cellulosic matter on the fibers is then almost instantaneous withsubstantially no more than the theoretical amount of gas required, whilemechanical destruction and chemical degradation of the ti'bers arereduced to an insigniiicant amount or practically eliminated.

Conventional treatment of unbleached pulps is a slow and cumbersomeprocess inasmuch as it requires very large expensive treatment towersprovided with lbuilt-in propeller type agitators and an expensivenon-corrosive inner lining, along with washing iilters, heaters, pumpsand instrumentation such yas sensing instruments and the like. The pulpin a relatively ldilute state containing the dissolved treatment agentat great dilution is required to undergo the desired reaction whilepassing relatively slow-4 ly through this treatment tower during aperiod of detention which may be hours.

With these treatment towers, the lower the consistency of the pulp, thegreater is the detention time required for consummating the reaction. Onthe other hand, increases in consistency may render the reactionditiicult to control, inasmuch as excessive degradation of the cellulosebers may occur incident to the reaction at these higher consistenciesand at greater concentration of the reagents and of the reactionproducts. The relatively low consistency at which the pulp musttherefore undergo reaction in the treatment towers makes vfor largetower size requiring high capital outlays, maintenance as well as space.

Conventionally, as an example of a complete treatment brown stock havinga consistency of only 31/z% and containing the chlorine in solutionpasses through th rst treatment tower preferably in upllow fashionrequiring a detention time of about one hour which allows most of thelignins on the lbers to react with chlorine, the reaction productingchloro-lignins. The solubility of these chlorolignins depends upon themolecular weight, in the sensef that the low molecular weightchloro-lignins vare rendered soluble by chlorination only whereas thehigher molecular weight chloro-lignins are solubilized by a certainamount of oxidation and forming soluble compounds such as sodium salt.Among other dissolved chlorine reaction products is HC1 which latter ispotentially destructive t0 `fibers but appears at sutliciently lowconcentration. Hence, the chlorine-reacted pulp usually overflowing fromthe top end of the tower is then washed free of the HC1 and otherreaction products as on a washing iilter. This chlorination operationproduces a shrinkage due to removal of undesirable material which is inthe order of 5% The chlorine-reacted washed lilter cake must be repulpedso that it may `be subjected to the next treatment step called alkalineextraction conventionally by hot weak NaOH solution in another towertreatment. This will solubilize the high molecular weightchloro-lignins, yet with an attendant shrinkage due to removal ofundesirable material of about 2%% with the stock concentration in thetower being kept as of a suitable 12% and also with the concentration ofthe caustic such as to minimize tibet degradation. The resultingreaction products again must 'be washed out as in a washing lilteroperation, the washed filter cake to be repulped for still another towertreatment step. The pulp having been freed by the preceding twosuccessive tower treatments from most of its lignins as well as othernon-cellulosic matter, may be subjected for example in a third or lasttower treatment step to the action of bleaching agent such as calcium orsodium hypochlorite with the stock consistency kept at a suitable 12% to16%. This treatment not only bleaches the tibers but also oxidizes andremoves residual lignins from the bers but with a shrinkage due toremoval of undesirable material to the extent of about 21/z%. Here thedetention time which may be from l to 6 hours, must be long enough toallow the oxidized lignins to diffuse out from the fibers so they canagain be washed out in a iinal washing filter operation.

This invention makes it possi-ble to have bulky and expensive treatmenttowers as well as various other equipment partly or entirely eliminated,and the respective reaction or reactions themselves speeded upenormously, even while avoiding fiber degradation as by any of thereaction products or otherwise. Such radical improve# ments areaccomplished by way of subjecting the un bleached pulp to a dewateringoperation increasing the' pulp consistency at least to a ldegree whichmay be 20% to 30% consistency where the fibrous elements rather than theliquid control the physical characteristics of the fibrousmass, and thepulp is rendered directly in the form of tibrousclusters or uied upflocs. This centrifugal treatment is such that the fibers remainsubstantially Hundamaged or unbroken even while retaining their naturalspringiness, so that each such cluster represents a spongy structurethat is resiliently compressible and can be readily and instantaneouslypenetrated by a treatment gas adapted to react instantaneously lwith therespective non cellulosic matter on the iibers.

For example, if chloriner is initially applied in its gaseous state to apulp that has been prepared in the manner of this invention, chlorinereaction with the non-cellulosic matter in the illocs is consummatedwithin a contact time that may be in the order of mere `fractions of asecond as compared with hours of conventional tower treatment. Anyappreciable chemical Adegradation of the fibers therefore has no chanceto manifest itself especially if the rei-4 action is promptly -followedby a wash. The physical characteristics of the prepared stock or pulpare such asv to permit instantaneous penetration of the clusters alsobythe washing and repulping liquid.

The librous product having the particular qualiiications above setforth, is obtainable according to one embodiment by subjecting astarting pulp, for instance brown stock of owable consistency, tocentrifugal separating forces by feeding a continuous supply of pulpinto the inlet end of a centrifugal screen device. Thus, there isinitially formed upon the inside of the inlet end a blanket of fibersfrom which the liquid is centrifugally drained through the screen. Whileunder the influence of these centrifugal forces, suitable slow-actingimpelling means within the screen disrupt the initially formed blanketsubdividing the same into the aforementioned discrete clusters or spongyfibrous structures even while moving the same continuously and gentlytowards the discharge end of the rotary screen for delivery therefrom asa dewatered and prepared stock which may vhave a consistency of from 20%to 30%. Meanwhile, the separated liquid discharges along another pathfrom this machine.

The method of treating the prepared stock with the gas according to oneembodiment, comprises maintaining in a treatment chamber a iiow of thetreatment gas, continuously feeding to the chamber a controlled quantityof the unbleached pulp or stock, continuously moving the stock throughthe chamber preferably counter-current to the flow of treatment gas, andaccordingly discharging the treated stock from the chamber still in theform of clusters lfor repulping and for washing. Thus, untreatedclusters of prepared stock may enter the chamber at one end thereof,while gas-treated clusters discharge from the other end. The controlsmay be such that substantially of the gaseous reagent is absorbed in thereaction.

According to one feature, a slight vacuum is applied to the contents ofthe chamber under conditions so controlled that highly efficient as wellas rapid reaction between the gas and the non-cellulosic matter may beobtained.

Other 'features lie in employing gaseous reagents in treatment stepsfollowing chlorination thereby similarly eliminating conventionaltreatment towers and accessory equipment, with gassing treatmentadvantages similar to those set forth above.

Apparatus for practicing the foregoing method of reacting material withthe gas, features combined metering and conveying means wherein anendless sequence of spaced gas-permeable partitions move through areaction chamber. In a preferred form, the apparatus resembles a starfeeder mechanism altered for the purposes of this invention, which maybe combined directly with the centrifugal screening device so as toconstitute therewith a compact operating unit replacing not only thereaction towers but also cumbersome washing lilter and repulpinginstallations.

Features of the apparatus relate to Washing and repulping meanscompactly arranged in direct association with the gas reactor. Stillother features and advantages will hereinafter appear.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof` willbe best understood from the following description of specific embodimentwhen read in connection with the accompanying drawings, in which: FIG. 1is a vertical sectional view of a centrifugal screen yfor dewatering andpreparing the stock in accordance with the requirements of thisinvention;

FIG. 2 is a vertical sectional view of apparatus in a preferred Iformfor effecting the reaction between pulp and gas in a continuouscounter-current fashion, directly combined with washing and repulpingmeans;

FIG. 3 illustrates, in a preferred arrangement, the application of thisinvention to a sequence of cooperating treatment steps each involvingthe treatment of the specially prepared stock with a gas;

FIG. 4 completes the arrangement of FIG. 3 by the addition of a nalcentri-fugal dewatering and pulp conditioning stage;

FIG. 5 is a somewhat enlarged photographic view of the fibrous productdelivered by the screening centrifuge, and having the special physicalcharacteristics called for by this invention; Iand FIG. 6 is amicroscopic view of the cellulose bers after repulping of the fibrousproduct illustrating the absence of short fibers or debris in thepreservation of the fibers.

Since the invention revolves around the problem of speciallyconditioning the unbleached pulp, for example lbrown stock, fortreatment with a gaseous reagent, reference may first be had to theprepared pulp material as shown in the photograph in FIG. 5. This showsthe ulfed up flocs or clusters presenting fibrous spongy structureswhich according to the invention result when the unbleached stock issubjected to the dewatering treatment in a centrifugal screen device anexample of which is shown in FIG. 1.

According to the invention, the fibrous product thus obtained is ideallysuited for treatment with a gaseous reagent such as chlorine as Well asother gases as will be furthermore explained. Even though with about 70%moisture left in it, and thus at a consistency of 30%, this fibrousproduct presents a iluiied-up dry appearance. In bulk, it appears as amass of individual clusters or rolls in each of which the fibers aresubstantially contained in an undamaged state having retained theirnatural springiness so that it is one of the physical characteristics ofthis product that these clusters or fibrous units in fact areresiliently compressible. Each such cluster or roll is an average of 1%"or 10 mm. long, more or less. This librous product as `a mass can bereadily handled and bagged or put up in suitable containers to beshipped for treatment as in a different locality. However, in apreferred form of operation, this material can be delivered continuouslyfrom the centrifugal screen device directly into the reactor fortreatment counter-current with the gaseous reagent.

- The centrifugal screen device for so dewatering and speciallyconditioning the stock into the illustrated fluifed up flocs of FIG. 5may be of a suitable known design orv type such as exemplified in FIG.1.

In such a machine the centrifugal screen mechanism 10 proper is enclosedin housing 11 which has a transverse dividing wall 12 which togetherwith the screen mechanism 10 defines an upper volute chamber 13 surrounding the screen to receive the centrifugally separated liquid fordischarge through an outlet neck 12a, and a lower chamber 13a into whichdischarge the solids retained by the screen in the form above indicatedand illustrated. In this example, the feed suspension or pulp enters thenarrow end of the conically shaped screen construction 14 at once to besubjected therein to the centrifugal forces which drain the liquidthrough the screenA into the surrounding volute-chamber as indicated by'arrows A1 While a conical screw member 15 shaped toy conform to theinner conical face of the screen and rotating at a slightly higher speedcontinuously transports the solids on the screen towards the wide endthereof for discharge into the lower chamber 13a formed with ahopper-shaped bottom 16 having a downward discharge neck 17.Morespeciiically, the screen construction 14 in the machine hereinexemplified comprises a conical screen element 1S proper mounted withina correspondingly shaped, perforated backing member 18a for rotationtherewith, which backing member in turn is carried bya hub member 19through ribs 19a unitary with a hollow shaft 20 mounted for rotation insupporting structure 21 which in turn is supported in the lower chamber13a of the housing. The conically shaped screw member is fixed to aquill shaft 22 which is mounted for rotation concentric within thehollow shaft that rotates the screen. Drive means 23 are indicated forimparting to both screen 18 and the co-operating screw member 15 therequired differentiated speeds.

While the physical characteristics of the prepared fibrous product asobtained from the centrifugal screening is such that it may readily beput up in bulk and transported to another locality for treatment with agaseous reagent, preferably the material is delivered directly from thescreening device into a reactor which, like the screening device, mayoperate continuously and one form of which is illustrated in FIG. 2.

in this reactor, the prepared stock is moved through a reaction chambercounter-current to the flow of gas, under conditions so arranged as toprevent the gas escaping through the inlet or through the outletpassages through which the material respectively enters and dischargesfrom this reaction chamber. According to the invention, the effect ofthe gas may be confined to a reaction zone located between a gas inletwhere slight .pressure is maintained and a gas outlet to which a slightvacuum is applied, with the bulk of the material present in the reactionzone accounting for the pressure differential between the gas inlet andthe gas outlet means. An endless sequence of gas-pervious partitionsspaced equally from one another move through the reaction zone formingwith the walls of the reaction chamber a corresponding sequence ofcompartments containing substantially .equal amounts of the material,thus moving the material .through the reaction zone.

With these features in view, the reactor exemplified in FIG. 2 isconstructed as a compact treatment unit resembling a star feeder devicealtered and adapted to the purposes of this invention.

Accordingly, this reactor comprises a star wheel 24 mounted for rotationabout a horizontal axis in the end walls of a cylindrical housing 25which at the top is formed with a fianged inlet 26 connected directly tothe discharge neck of the centrifugal screening device above. Theflanged outlet 27 discharges gas-treated material from the reactor intoa repulper 28 preferably connected directly to the outlet 27 of thereactor.

The star wheel 24 has a cylindrical rim portion 29, rigidly connected byspokes 30 to a hub 31 which in turn is fixed upon a shaft 32 rotatablein the end walls of the housing 2S. The rim portion 29 has radiallyextending gas-pervious partitions 33 angularly spaced from one anotherequal distances defining a sequence of compartments and provided withperforations 34 or the like indicating passages through which the gasmay pass from one compartment 35 to the next in counter-current to thematerial carried in the compartments through the reaction zone.

Adiacent to the discharge outlet 27 the housing has a ygas inlet 36,whereas adjacent to the inl-et 26 for the prepared material there is agas outlet 37. Rotation of the star wheel 24 as by a motor drive notshown in the direction indicated by arrow A3, will cause the gasperviouspartitions to move corresponding Quantities of the material continuouslyinto and through the reaction zone located within the angle Z betweenthe inlet and outlet for the gas. As the material moves through thisreaction zone, the slight suction maintained at the gas outlet 37 atleast partially removes air from the interstices of the prepared stockthereby relatively increasing the effectiveness of the gaseous reagent.A very high degree of effectiveness in terms of reaction speed and avery high degree of efficiency in terms of gas utilization are thusobtainable if the speed of rotation of the wheel 24 governing the rateof movement of the material through the reaction zone, and the supply ofgas, are so controlled with respect to each other that substantially allthe gas will have been utilized during passage of the material throughthe reaction zone. With such control it becomes 6 possible in fact tocarry out the reaction with only the theoretical amount of gaseousreagent required and within a space of time within this zone which as inthe case of chlorine is in the order of fractions of a second. Hence,under such conditions practically none of the treatment gas itself wouldreach the gas outlet 37.

With the treated material from the reactor discharging substantially insame physical condition as the prepared product which was supplied tothe reactor, into the repulper 28, repulping wash water is at once addedso as to block degradation such as lthe reaction products mightpotentially exert towards the degradation of the bers. 1For that purposethere is shown a ring shaped supply header 38 surrounding the outlet 27,provided with inwardly directed radial branch connections 39 fordelivering water into the transfer passage between the reactor and therepulper. Additionally, a valved supply pipe 40 is provided terminatingin this passage area for directing a jet of wash water upwardly intorespective compartments 35 as they move past the outlet 27, insuringthat all of the material be flushed out thoroughly from thecompartments, thus conditioning them for refill in their cyclic path ofmovement.

The repulper 28 according to a preferred example comprises a horizontalconveyor screw 41 which has a shaft 41a provided with supplementaryradial agitating arms 42, and journaled for rotation in the end walls ofa closed horizontal elongated casing y43 having at one end thereof ahanged inlet 44 whereby the repulper is preferably connected directly tothe reactor outlet 27. This repulper casing has a flanged outlet 44awhich may be connected to a pump for transferring the treated andrepulped material to a subsequent treatment station, or as illustratedin FIG. 4 directly to another centrifugal screen device 'C fordewatering and conditionijng preparatory to further treatment orpreparatory to shipment of the product or else the repulper maydischarge into a storage bin or the like.

ln the purification treatment of unbleached pulp, the invention may beapplied to one or more of a sequence of treatment steps. However, in theexample of a complete treatment shown in kFIG. 3 the invention isutilized in each one of a combination of steps comprising in sequencethe chlorination, the alkaline extraction, and the oxidation bleachingstage. Yet, it will be understood that the invention is in no waylimited to these treatment steps either relative to kind or relative tosequence or relative -to the number of treatment steps.

According to the example of a complete treatment shown in FIG. 3, theinitial unbleached stock which may be -brown stock, is fed at a pumpableconsistency range to a first centrifugal screening device 45 which maybe oney in FIG. 2, whereby it is ldewa-tered and possibly washed andwhich converts the pulp into the relatively dry prepared product hereindescribed and illustrated. The thus prepared material dischargesdirectly into a first reactor 46 to which chlorine gas is fed at '47 viaa control means or valve 48 to react with the stock, While suction isapplied at 49. In the case of chlorine, a reaction time of about W10 ofa second was found to be sufficient forY the reaction to be completedunder the conditions provided for by this invention as set forth. 'Fromthis reactor, the chlorinated `stock drops into a first repulper 51which may be the one shown in FIG. 2, while repulping water is addedthrough pipe 52. in an amount regulated as by a valve 53 or the like.From the repulper -the stock is then transferred as by a first pump 54and a conduit 55, into a second centrifugal screening device 56operating substantially in the same manner as the one inthe firsttreatment stage and delivering a fibrous product of similar physicalcharacteristics prepared and suited for treatment with another gas. FIG.4 illustrates an alternative arrangement wherein the prepared stock fromthe repulper S1 may he discharged into a next following centrifugalscreening device designated yby the let- 7 ter C. In this stage,according to the invention, gaseous NH3 may be applied in the reactorfor the purposes of alkaline extraction in a second reactor. 57 whichmay be similar to the one in the first treatment stage. Again, theresulting treated stock is at once rediluted and repulped in a secondrepulper 58 resembling the one of the first treatment stage. Il-"romthis repulper 58 a second pump 59 with conduit 60 may transfer therepulped stock to a third centrifugal screening device 66a whichprepares the pulp in the manner of the preceding stages for treatmentwith gaseous oxidizing bleaching agent. IIn this last treatment stage,the bleaching treatment according to the invention may be carried outfor example by means of C102 in its gaseous state in a third reactor 61which may resemble those in the preceding treatment stages. Suitably,since pure C1102 is explosive, it is supplied adequately diluted with aninert gas preferably so that the partial pressure of the C102 is at alltimes below 200 mm. Hg. In this last reactor 61, the detention time willbe long enough, in the order of minutes, if the C102 gas suitablydiluted is to be absorbed substantially completely by the preparedmaterial, whereupon the material instead of going directly to a repulpermay be conveyed to a storage chest or other storage facilities withoutdilution there to allow for a period of time suitable for completingreaction with the absorbed C102. Wash water may be added in each of thecentrifugal screening stages of the operation. Yet, other gaseousoxidizing bleaching agents may be used of which ozone is an example,ozone by its nature being a highly effective bleaching agent.

In each one of the treatment stages just described in vconnection withthe example of FIG. 3, the manner of centrifugally preparing the stockrenders the same in the form of physical condition substantially asabove described and as illustrated in FIG. 5, and thereby eminentlysuited for effective treatment with respective gaseous reagents withoutinflicting any significant mechanical damage to the fibers due to theabsence of any mechanical squeezing or compressing action. The metricscale shown in FIG. 5 in millimeters provides an indication of theactual size of the clusters of brous flocs produced by the centrifugaloperation. Yet, the condition of the prepared stock is equally favorablewith respect to the repulping operation, in that the fibers ,willreadily separate from one another and in fact have been observed Itofloat apart in the diluting water without damage to the fibers. This isin accordance with the micro-photograph of FIG. 6 representing anunbleached pulp in a state of redilution after it had been prepared in acentrifugal screening device in a manner herein set forth.

From the foregoing, it will be seen that the discovery underlying thisinvention makes it possible to convert fibrous cellulose pulp rapidlyfrom a dilute condition into a relatively dry product that readily lendsitself for almost instantaneous penetration by a treatment gas, asdistinct from tower treatment with solutions, thereby affordingimmediate contact and substantially instantaneous reaction of the gaswith non-cellulosic matter on the fibers. In this way, inasmuch as oneor more of the conventional reaction towers as well as other expensiveapparatus may be eliminated by this invention, the installed cost aswell as the space requirements of apparatus embodying the invention isstartingly reduced. At the same time, an equally startling reduction inreaction time as Well as minimum requirements in reagent chemical areachieved along with practically no degradation of the fibers chemicallyor mechanically. A high-grade final fibrous product can thus be providedwhich in turn makes for a high-strength, high-quality paper product.

For example, the invention may be applied to any one or more of a seriesof required treatment steps. Therefore, the invention may be applied toa partially bleached stock.

Also, the treatment may be terminated after any one stage wherein thestock has been treated in accordance with the teachings of thisinvention, namely by contacting the specially prepared stock with agaseous reagent.

It will also be understood that the term gaseous reagent may hereininclude any suitable mixture of gases.

With respect -to the sequential treatment steps illustrated in FIG. 3 orany similar arrangement, it will be understood that the transfer pumpsbetween the stage may be eliminated by arranging the respectivetreatment steps for direct gravitational discharge of the prepared pulpfrom one stage to the next, that is from any one repulper directly intothe next following centrifugal screening unit.

Moreover, the term continuous as herein used with respect to practicingthe method or running the apparatus, includes not only an uninterruptedflow but also an intermittent flow at such frequencies that the effectis that of a substantially continuous flow for the purposes of thisinvention.

l claim:

l. Apparatus for the `continuous treatment of fibrous stock with agaseous reagent, comprising a reaction chamber provided with stock inletand outlet means for passing therethrough the stock which has beendewatered so as to be rendered in a relatively dry condition, saidchamber also having gas inlet and outlet means arranged incounter-current relationship to said stock inlet and outlet means; andcombined metering and conveying means for passing said stock throughsaid chamber in such a manner as to cause said gaseous reagent topenetrate the material to react with non-cellulosic constituents thereofwhile passing counter-currently therethrough, said cornbined meanscomprising an endless sequence of gas-permeable partitions movable at acontrolled rate through said reaction chamber and defining between themand with the walls of the chamber a corresponding sequence ofcompartments adapted to contain a sequence of coniined volumes of saidstock while moving through said chamber counter-current to said gaseousreagent, so that incident to the movement of said endless sequence ofpartitions a sequence of lled compartments moves from said stock inletto said stock outlet means while emptied compartments vmove from saidstock outlet to said stock inlet means. Y

2. The apparatus according to claim 1, with the addition of a suctionconnection provided in the region of said stock inlet means to effectair evacuation for improving the subsequent penetration by the gas intothe stock.

3. Apparatus for the continuous treatment of fibrous stock with `agaseous reagent, comprising a cylindrical casing having a peripheralwall and transverse end walls, provided with a stock inlet and a stockoutlet connection on said peripheral wall for passing therethroughunlbleached stock which has been dewatered so as lto be rendered in arelatively dry condition, said casing also having gas inlet and outletmeans arranged in countercurrent relationship to said stock inlet andVoutlet connections; and combined metering and conveying means forpassing said stock through said chamber in such a manner as to causesaid gaseous reagent to penetrate the material to react withnon-cellulosic constituents thereof while passing counter-currenttherethrough, said combined means comprising a rotary transportingmember turnable at a controllable rate in said casing co-axialtherewith, and having gas-pervious partitions extending radiallytherefrom angularly substantially equally spaced from one another andco-operative with the walls of the casing to constitute an endlesssequence of compartments adapted to carry stock from said stock inletconnection to said Stock outlet connection, so that incident to therotation of said transporting member a sequence of filled compartmentsmoves from said inlet to said outlet while emptied compartments movefrom said outlet to said inlet .connection for re-iilling.

4. The apparatus according to claim 3, with the addition of meansdirectly associated with said stock outlet connection for introducingwast; water into the treated stock during its discharge from saidcompartments. g

5. The apparatus according to claim 3, withythe addition of meansdirectly associated with said stock outlet connection for introducingwash water into the treated stock during its discharge from saidcompartments, comprising upwardly directed nozzle means located withinthe passage area of said connection.

6. The apparatus according to claim 3, with the addition of a repulpingdevice connected to said stock outlet connection so that treated stockwill discharge directly into said repulping device by gravity, saidrepulping device comprising a horizontal conveyor screw, and means forintroducing wash water into the treated stock for repulping.

7. The apparatus according to claim 3, with the addition of a verticallydisposed centrifugal screen unit having a housing providing -a reservoirhaving a bottom discharge neck connected to said stock inlet connectionfor gravitationally delivering thereto said dewatered stock.

8. Apparatus for the continuous treatment of fibrous stock with agaseous reagent, comprising a reaction chamber provided with stock inletmeans and outlet means for passing therethrough the stock which has beendewatered so as to be rendered in a relatively dry condition, saidchamber also having gas inlet and outlet means arranged incountercurrent relationship to said stock and outlet means; combinedmetering and conveying means for passing said stock through said chamberin such a manner as to cause said gaseous reagent to penetrate thematerial to react with non-cellulosic constituents thereof while passingcountercurrently therethrough, said combined means comprising an endlesssequence of gas-permeable partitions movable at a controllable ratethrough said reaction chamber and defining between them and with thewalls of the chamber a corresponding sequence of cornpartments adaptedto contain a sequence of confined volumes of said stock while movingthrough said chamber countercurrent to said gaseous reagent, so thatincident to the movement of said endless sequence of partitions asequence of filled compartments moves from said stock inlet to saidoutlet while emptied compartments move from said outlet to said inletconnections for re-filling; and a vertically disposed centrifugal screenunit having a housing providing a reservoir having a bottom dischargeneck connected to said inlet connection for delivering thereto saidprepared stock.

9. The apparatus according to claim 8, with the addition of a repulpingdevice connected to said stock outlet connection of said reactionchamber so that treated stock will discharge directly into saidrepulping device by gravity, said repulping device comprising ahorizontal conveyor screw, and means for introducing wash water into thetreated stock for repulping.

10. The apparatus according to claim 8, with the addition of a repulpingdevice connected to said stock outlet connection of said reactionchamber so that treated stock will discharge directly into saidrepulping device by gravity, said repulping device having a downwarddischarge neck, means for introducing wash water into the treated stockfor repulping, and another vertically disposed centrifugal screen unithaving its top end connected to said downward discharge neck to receiverepulped treated stock for centrifugal dewatering.

ll. The method of treating fibrous cellulosic stock with a gaseoustreating agent, which comprises continuously dewatering the stock bypassage through a continuously operating centrifugal screen providedwith helical discharge screw to a consistency where the fibrous elementsof the stock rather than the liquid control the physical shape of thefibrous mass, with the helical screw cooperating with the screeneffective to continuously discharge the dewatered material in the formof discrete clusters 1 0,., of lfibrous. elements constituting spongystructures wherein the fibers haveretained their natural resiliency, andwhich clusters are thereforesubject to uniform gas penetration;continuously supplying such clusters to a gas reaction chamber throughwhich is kept passing a continuous flow of treatment gas', continuouslymoving said clusters through said chamber at a substantially uniformcontrolled speed in counter-current to said flow of gas reactinguniformly therewith because of said uniform penetration; and subjectinggas-treated clusters to repulping and to washing.

l2. The method according to claim 1l, wherein said treatment gas is froma group comprising chlorine, chlorine dioxide, and NH3. j vi3. Themethod according to claim v1l, wherein air is evacuated from the voidsin said clusters by maintaining a vacuum in said chamber in the regionof the entrance of said clusters into said chamber to facilitate thesubsequent penetration of said clusters by said gaseous reagent.

f4. The method of continuously treating fibrous stock with a gaseousreagent, which comprises providing a supply of said stock dewatered bycontinuous centrifugal screening effects to a consistency where thefibrous elements of the stock rather than the liquid control andphysical shape of the fibrous mass, so that the material is in the formof discrete clusters of fibrous elements, constituting spongy structureswherein the fibers have retained their natural resiliency, and whichclusters are therefore subject to uniform gas penetration; andsubjecting said clusters to reaction with said gaseous reagent in a gastreatment zone effecting uniform reaction because of said uniform gaspenetration of the clusters, said gas treatment comprising continuouslysupplying said clusters to a gas reaction chamber through which ispassing a continuous fiow of treatment gas, continuously moving saidclusters through said chamber at a substantially uniform controlledspeed in counter-current to said flow of gas; and repulping and washingthe gas treated clusters.

l5. The method of continuously treating fibrous stock with a gaseousreagent, which comprises providing a supply of said stock dewatered bycontinuous centrifugal screening effects to a consistency where thefibrous elements of the Stock rather than the liquid control thephysical shape of the fibrous mass, so that the material is in the formof discrete clusters of fibrous elements, constituting spongy structureswherein the fibers have retained their natural resiliency, and whichclusters are therefore subject to uniform gas penetration; andsubjecting said clusters to reaction with said gaseous reagent in a gastreatment zone effecting uniform reaction because of said uniform gaspenetration, said gas treatment cornprising continuously supplying suchclusters to a gas treatment chamber through which is passing acontinuous ow of treatment gas, continuously moving through said chambera sequence of confined metered quantities of said clusters incounter-current to said fiow of gas passing sequentially through saidquantities within the bounds of their confinements, whereby said gaswill penetrate the spongy structures of the fibrous clusters even whensubstantially at rest with respect to one another; and repulping andwashing said gas treated clusters.

16. The method of treating fibrous stock with a gaseous bleachingreagent, which comprises providing a supply of said stock prepared forthe reaction by passing said stock through a continuously operatingcentrifugal screen provided with a discharge screw concentric with saidscreen for dewatering the stock to a consistency where the fibrouselements of the stock rather than the liquid control the physical shapeof the fibrous mass, so that the material delivered by the screen is inthe form of discrete clusters of fibrous elements formed simultaneouslywith the centrifugal dewatering operation by the coaction of thedischarge screw and the screen, the resulting clusters constitutingspongy structures wherein the fibers have retained their naturalresiliency and which clusters are therefore readily and uniformlypenetrable by said gaseous reagent; maintaining said prepared stock insaid chamber exposed to said gaseous reagent for a length of timesucient to attain uniform reaction between the fibers and the gaseousreagent as a result of said uniform gas penetration into the voids ofthe clusters whereby inadequate reaction of the fibers in the interiorportion as Well as excessive destructive reaction of the peripheralportion of the clusters is avoided when subjected to said penetration;and repulping and washing the reacted stock.

17. The method according to claim 16, wherein air is evacuated yfrom thevoids in said clusters suiciently to facilitate subsequent penetrationthereof by said gaseous reagent.

References Cited in the tile of this patent UNITED STATES PATENTS

11. THE METHOD OF TREATING FIBROUS CELLULOSIC STOCK WITH A GASEOUSTREATING GENT, WHICH COMPRISES CONTINUOUSLY DEWATERING THE STOCK BYPASSAGE THROUGH A CONTINUOUSLY OPERATING CENTRIFUGAL SCREEN POVIIDEDWITH HELICAL DISCHARGE SCREW TO A CONSISTENCY WHERE THE FIBROUS ELEMENTSOF THE STOCK RATHER THAN THE LIQUID CONTROL THE PHYSICAL SHAPE OF THEFIBROUS MASS, WITH THE HELICAL SCREW COOPERATING WITH THE SCREENEFFECTIVE TO CONTINUOUSLY DISCHARGE THE DEWATERED MATERIAL IN THE FORMOF DICRETE CLUSTERS OF FIBROUS ELEMENTS CONSTITUTING SPONGY STRUCTURESWHEREIN THE FIBERS HAVE RETAINED THEIR NATURAL RESILIENCY, AND WHICHCLUSTERS ARE THEREFORE SUBJECT TO UNIFORM GAS PENETRATION; CONTINUOUSLYSUPPLYING SUCH CLUSTERS TO A GAS REACTION CHAMBER THROUGH WHICH IS KEPTPASSING A CONTINUOUS FLOW OF TREATMENT GAS; CONTINUOUSLY MOVING SAIDCLUSTERS THROUGH SAID CHAMBER AT A SUBSTANTIALLY UNIFORM CONTROLLEDSPEED IN COUNTER-CURRENT TO SAID FLOW OF GAS REACTING UNIFORMLYTHEREWITH BECAUSE OF SAID UNIFORM PENETRATION; AND SUBJECTINGGAS-TREATED CLUSTERS TO REPULPING AND TO WASHING.